Keeping Cool

Kenneth E. Robinson, CIH Apex, N.C.

Sun, 2009-11-01 12:00

Three facilities — a warehouse, forge plant, and paint-preparation area — had complaints about excessive heat in working areas. I recommended that air be brought in from outside and distributed 10 ft above the floor in the warehouse and paint-preparation area. Because of the forge plant's excessively high temperatures, 4,000-cfm air was to be supplied at each workstation through outlets located 30 in. above the floor. I also recommended that an evaporative cooler (EC) be installed in each facility's supply system.

The dry-bulb (DB) temperature of the air leaving an EC is determined by the wet-bulb (WB) temperature of the surrounding air. If an EC is 100-percent efficient, air leaves the unit at WB temperature. The efficiency of a double-bank EC should be over 90 percent. Because studies have determined that WB temperatures in most cities do not exceed 80°F during summer, a safe assumption is that the WB temperature of outside air would be 78°F when the DB temperature is 90°F. Air that is 90°F is only 6°F below skin temperature, which would not provide adequate cooling to prevent occupant stress. If outside air were passed through a 90-percent-efficient EC first, the DB temperature of the leaving air would be 80°F. If that air — 16°F below skin temperature — were distributed in an occupied space at a velocity of 200 fpm or more, cooling would be adequate.

After the facilities' EC systems were installed, I visited the warehouse on a hot day and did not hear any complaints about the temperature. When I visited the forge plant on an 82°F day, I realized the EC was not running. When I questioned the employees, they said the EC was not turned on until it warmed up outside. I was told they had an agreement with management that if the EC was not operable on a hot day, the employees did not have to work. Nonetheless, since the EC had been installed, production was the same on a hot day as it was during winter; prior to its installation, as much as half of the production was lost on a hot day.

Although I was not able to revisit the paint-preparation area, I received a letter from the manager thanking me for my help. He said the installation I had designed had produced an even better environment than I had indicated.